There are several technologies for a conventional wireless communication system.
For instance, in a radio communication system composed of an access point and plural user terminals, the same frequency may be used for plural user terminals to transmit data to the access point at the same time, i.e., SDMA, as disclosed in US Pat. Application No. 2005/01115999A1.
In addition, Orthogonal Frequency Division Multiplexing (OFDM) is used as a conventional modulation/demodulation method for realizing high-speed wireless data transmission (Eduardp F. Casas, Cyril Leung, “OFDM for Data Communication Over Mobile Radio FM Channels Part I: Analysis and Experimental Results”, May, 1991, IEEE Transaction on Communications Vol. 39, No. 5, pp. 783-793).
Moreover, the IEEE802.11 standard exists as a conventional wireless LAN system using the OFDM (IEEE Std 802.11a-1999, IEEE, IEEE Std 802.11g-2003, IEEE).
Also, there is Multiple-Input Multiple-Output (MIMO) wireless LAN system, a system using the OFDM for modulation (TGn Sync Proposal Technical Specification, May 13, 2005, IEEE802.11-04/0889r5).